Discrete Wavelets and Image Processing

Transcription

1 Discrete Wavelets and Image Processing Helmut Knaust Department of Mathematical Sciences The University of Texas at El Paso El Paso TX October 16, 2009

2 Math 5311: Applied Mathematics Course Objectives Course Objectives: Get a flavor of the ideas and issues involved in applying mathematics to a relevant engineering problem Develop an understanding of the theoretical underpinnings of wavelet transforms and their applications Learn how to use a computer algebra system for mathematical investigations, as a computational and visualization aid, and for the implementation of mathematical algorithms

3 Math 5311: Applied Mathematics Prerequisites Prerequisites: A thorough understanding of Calculus Some familiarity with matrices Mathematical maturity Willingness to learn Mathematica

4 The Problem The Engineering Problem: Transmit digital information through a narrow channel. Lossy compression : The information received need not be identical to the one sent, but the quality must be acceptable. Channel

5 The Problem Applications: Photos MP3 players Real-time two-way audio (cellular telephones)

6 The Problem Applications: Photos MP3 players Real-time two-way audio (cellular telephones) Streaming video (Netflix, Hulu)

7 The Problem Applications: Photos MP3 players Real-time two-way audio (cellular telephones) Streaming video (Netflix, Hulu) Real-time two-way audio and video (Skype)

8 Discrete Wavelets and Image Processing Basics of Digital Signal Processing A color image consists of three color channels: Red, Green and Blue

9 Basics of Digital Signal Processing Each pixel in a gray-scale image is represented by an integer between 0 and 255 = (8 bit = 1 byte) 0=black, 255=white

10 Basics of Digital Signal Processing Raw storage requirement: ( ) bytes = KB

11 Basics of Digital Signal Processing Naive compression Average of four neighboring pixels: Compression factor: 4

12 Approximating data Mathematical Question: What ways are there to approximate a function ( data ) other than just averaging?

13 Approximating data Mathematical Question: What ways are there to approximate a function ( data ) other than just averaging? Differentiation Techniques

14 Approximating data Mathematical Question: What ways are there to approximate a function ( data ) other than just averaging? Differentiation Techniques Taylor series

15 Approximating data Mathematical Question: What ways are there to approximate a function ( data ) other than just averaging? Differentiation Techniques Taylor series Integration Techniques

16 Approximating data Mathematical Question: What ways are there to approximate a function ( data ) other than just averaging? Differentiation Techniques Taylor series Integration Techniques Fourier series Wavelets

17 Approximating data Fourier techniques Fourier approximation Π 3 Π 4 Π 2 Π Π 4 Π 2 3 Π 4 Π sin(t) sin(2t) sin(3t) sin(4t) sin(5t) sin(6t) cos(t) cos(2t) cos(3t) cos(4t) cos(5t) cos(6t)

18 Approximating data Fourier techniques Fourier series of the function f (t): a n sin nt + b n cos nt n=1 n=0 The coefficients are given by a n = 1 π π π f (t) sin nt dt and b n = 1 π π π f (t) cos nt dt (n 1)

19 Approximating data Fourier techniques The first Fourier functions:

20 Approximating data Fourier techniques The JPEG algorithm uses Fourier techniques - it employs the Discrete Cosine Fourier Transform (DCT). Here is a JPEG example with compression factor 6:

21 Approximating data Wavelet techniques Wavelet pioneers: Alfred Haar (t-r, on the left), Stephane Mallat (b-r), Ingrid Daubechies (t)

22 Approximating data Wavelet techniques The first Haar functions:

23 Approximating data Wavelet techniques Wavelet approximation: using the Daubechies-4 wavelet

24 Approximating data Wavelet techniques The basis functions are now re-scalings of the two functions below, the father wavelet (blue) and the mother wavelet (red)

25 Discrete Wavelets and Image Processing The JPEG2000 algorithm Original image

26 The JPEG2000 algorithm 1st color channel: Y

27 The JPEG2000 algorithm 2nd color channel: C r

28 The JPEG2000 algorithm 3rd color channel: C b

29 The JPEG2000 algorithm Applying the CDF97-wavelet transform to Y once

30 The JPEG2000 algorithm... and again...

31 The JPEG2000 algorithm... and one more time:

32 The JPEG2000 algorithm Quantizing the Y channel

33 The JPEG2000 algorithm The sender then encodes this quantized image and sends it through the narrow channel to the receiver. The compression factor in this example is The receiver then decompresses the image to be able to view the approximation of the original image.

34 Discrete Wavelets and Image Processing The JPEG2000 algorithm Undoing the transform (by receiver)

35 Discrete Wavelets and Image Processing The JPEG2000 algorithm Original image, again...

36 The JPEG2000 algorithm Zooming in on the original image:

37 The JPEG2000 algorithm Zooming in on the received image:

38 The JPEG2000 algorithm Any Questions?